Plasma apparatus and lower electrode thereof

ABSTRACT

The present invention is constituted of a lower electrode structure ( 1 ) comprising a base table ( 2 ) formed of a conductive material, an electrostatic adsorption member ( 3 ) formed on the base table ( 2 ) and having a dielectric layer ( 4 ) on which the substrate to be mounted and within which an electrode ( 5 ) electrically isolated from the base table ( 2 ) is housed, first wiring ( 7 ) having an end connected to the electrode ( 3 ) of the electrostatic adsorption member, a direct-current source ( 8 ) connected to the other end of the first wiring ( 7 ), second wiring ( 10 ) having an end connected to the base table ( 2 ), a high frequency source ( 11 ) connected to the other end of the second wiring ( 10 ), a third wiring ( 14 ) for connecting the first wiring ( 7 ) and the second wiring ( 10 ), and a capacitor ( 13 ) formed on the third wiring ( 14 ). Plasma processing is performed by disposing the lower electrode structure ( 1 ) in the chamber ( 21 ).

TECHNICAL FIELD

The present invention relates to a lower electrode structure used inapplying plasma processing, such as etching, to a substrate such as asemiconductor substrate. The present invention also relates to a plasmaprocessing apparatus using the lower electrode structure.

BACKGROUND ART

In a manufacturing process for a semiconductor device etc., processingwithin a high vacuum, such as a plasma etching, is frequently employed.However, when processing is performed under the high vacuum, vacuumadsorption cannot be used for holding a substrate such as asemiconductor substrate (hereinafter referred to as “wafer”) since thevacuum adsorption is usually applicable in the air. For this reason, thewafer is usually held by a mechanical means such as a clamp.

When the wafer is held by the clamp, the distal end of the clamp comesinto contact with an edge or a working surface of the wafer. As aresult, dust is generated at the time the clamp comes into contact withthe wafer and sometimes contaminates the wafer surface.

To overcome these problems, a holding means called an electrostaticchuck has been widely used.

FIG. 4 is a schematic view of a lower electrode structure having theelectrostatic chuck.

A lower electrode structure 100 shown in FIG. 4 has a susceptor 101formed of aluminium and an electrostatic chuck 102 formed thereon.

The electrostatic chuck 102 has a dielectric layer 103 having a mountingsurface for mounting a wafer W thereon and a flat electrode 104 arrangedin the dielectric layer 103. The susceptor 101 is connected to a highfrequency source 106 via a matching box 105. On the other hand, to aflat electrode 104, a direct-current source 108 is connected by way of alow pass filter 107.

In the lower electrode structure 100 having the aforementionedstructure, when a high frequency power is supplied from the highfrequency source 106 to the susceptor 101; at the same time adirect-current voltage is applied from the direct-current source 108 tothe flat electrode 104, electrostatic attraction such as a Coulomb forceis produced between the flat electrode 104 and the wafer W mounted onthe dielectric layer 103. As a result, the dielectric layer 103 attractsthe wafer W and holds it.

When such a lower electrode structure 100 is arranged in a chamber of aplasma processing apparatus such as a plasma etching apparatus, and thechamber is vacuumed, and then, a high frequency power is supplied fromthe high frequency source 106 to the susceptor 101, a high frequencyelectric field is formed in the vicinity of a working surface of thewafer W.

Thereafter, when a process gas is introduced into the chamber, a plasmaof the process gas is produced due to the high frequency electric field.The plasma is applied to the wafer W to perform plasma etching.

However, if the frequency of the high-frequency power to be suppliedfrom the high frequency source 106 to the susceptor 101 is, for example,2 MHz or less, the dielectric layer 103 interposed between the wafer Wand the susceptor 101 prevents the high frequency from passing through.As a result, the high frequency electric field is rarely converged onthe wafer W, decreasing etching characteristics. In particular, when thedielectric layer 103 is formed of ceramic, this tendency issignificantly observed.

Different from the lower electrode structure shown in FIG. 4 anothertype of lower electrode structure shown in FIG. 5 is known.

A lower electrode structure 110 differs from that shown in FIG. 4. Ahigh frequency power 106 is connected to a flat electrode 104 via amatching box 105 and a capacitor 11. The direct-current voltage from thedirect-current source 108 is superimposed on the high frequency voltagesupplied from the high frequency source 106 and then applied to the flatelectrode 104.

According to the lower electrode structure 110 mentioned above, adielectric layer 103 can pass a high frequency through it, compared withthe lower electrode structure 100 shown in FIG. 4, whereby the highfrequency electric field can be easily converged on the wafer W.

In the meantime, the heat conductivity under the high vacuum is lowerthan that under normal pressure, due to the extremely low amount ofheat-conductive medium. In the plasma processing performed under thehigh vacuum, a helium gas pipe 112 for supplying helium gas for heattransmission to a space between the wafer W and the dielectric layer 103is arranged, as shown in FIG. 5. Due to this, the temperature of thewafer W can be controlled even under the high vacuum.

However, the lower electrode structure shown in FIG. 5 has a problem inthat an abnormal discharge occurs within the helium gas pipe 112 whenhelium gas is supplied.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a lower electrodestructure capable of forming a high frequency electric field whichcapable of applying satisfactory plasma processing on a substratewithout an abnormal discharge and to provide a plasma processingapparatus using the lower electrode structure.

To attain the aforementioned object, the present invention provides alower electrode structure for use in an apparatus for applying plasmaprocessing to a substrate, comprising:

a base table formed of a material having a conductivity;

an electrostatic adsorption member formed on the base table and having adielectric layer on which the substrate to be mounted and within whichan electrode electrically isolated from the base table is housed;

first wiring having an end connected to the electrode of theelectrostatic adsorption member

a direct-current source connected to the other end of the first wiring;

second wiring having an end connected to the base table;

a high frequency source connected to the other end of the second wiring;

a third wiring for connecting the first wiring and the second wiring;and

a first capacitor formed on the third wiring.

The present invention provides a plasma processing apparatus comprising:

a chamber for applying plasma processing to a substrate while holdingairtight;

a lower electrode structure housed in the chamber and having a mountingsurface for the substrate;

an upper electrode arranged in the chamber so as to face the mountingsurface of the lower electrode structure;

an exhaust system for exhausting the chamber;

a process gas supply system for introducing a process gas into thechamber;

the lower electrode structure comprising

a base table formed of a conductive material

a dielectric layer formed on the base table and having a mountingsurface for the substrate;

an electrostatic adsorption member formed within the dielectric layerand having an electrode electrically isolated from the base table;

first wiring having an end connected to the electrode of theelectrostatic adsorption member;

a direct-current source connected to the other end of the first wiring;

second wiring having an end connected to the base table;

a high frequency source connected to the other end of the second wiring;

a third wiring for connecting the first wiring and the second wiring;and

a first capacitor formed on the third wiring,

wherein a plasma of the process gas is formed in the chamber by a highfrequency power output from the high frequency source and applied to thesubstrate, thereby performing a predetermined plasma processing.

In the present invention, the high frequency source is connected to thebase table by way of the second wiring and a high frequency voltage isapplied to the base table; on the other hand, the high frequency sourceis connected to the first wiring which connects the electrode of theelectrostatic adsorption member to the direct-current source, by way ofthe third wiring having a capacitor. Therefore, the high frequencyvoltage is superimposed on the direct-current voltage to be applied tothe electrode of the electrostatic adsorption member. Since the highfrequency voltage is applied not only to the base table but also theelectrode of the electrostatic adsorption member as described, the highfrequency can be effectively passed without being interrupted by theelectrostatic adsorption member. As a result, the high frequencyelectric field can be converged on the substrate, thereby performingsatisfactory plasma processing.

Furthermore, a high frequency voltage is applied by the third wiring toboth of the electrostatic adsorption member and the base table. However,due to the presence of a capacitor in the third wiring, a direct-currentvoltage is not superimposed on the second wiring. Since the phasedifference of the high frequency voltages to be applied to the electrodeof the electrostatic adsorption member and the base table can be reducedto a minimum, an abnormal discharge within the substrate can beprevented.

The abnormal discharge presumably occurs in the lower electrodestructure when the potential difference between members adjacent to eachother exceeds a predetermined value. When a direct-current voltage isapplied to the electrode of the electrostatic adsorption member and ahigh frequency voltage is applied to the base table, an extremely largepotential difference is periodically produced between the electrode andthe base table. As a result, an abnormal discharge occurs.

Under the circumstance, if the potential difference between theelectrode of the electrostatic adsorption member and the base table isconstantly set within a predetermined narrow range as described above,the abnormal discharge can be prevented even if a pipe for supplying aheat transmission gas such as helium gas, is formed within the basetable.

It is preferable that the present invention further comprise a capacitorwhich is formed on the second wiring and interposed between the basetable and a connecting point between the second wiring and the thirdwiring.

Since the capacitor is interposed, it is possible to control the phasesof the high frequency powers to be applied to the electrode of theelectrostatic adsorption member and the base table. If the phasedifference is reduced to a minimum, the abnormal discharge can beprevented.

In this case, if the phase of the high frequency to be applied to theelectrode of the electrostatic adsorption member is allowed to coincidewith that to be applied to the base table, the abnormal discharge can bemost efficiently prevented.

To describe more specifically, if the capacitor to be arranged to thesecond wiring has the same capacitance as that of the capacitor to beapplied to the third wiring, the impedance from the connecting pointbetween the second wiring and the third wiring to the flat electrode canbe made equal to that from the connecting point to the base table. As aresult, the phase of the high frequency to be applied to the electrodeof the electrostatic adsorption member is allowed to coincide with thatto be applied to the base table.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a lower electrode structure according toan embodiment of the present invention.

FIG. 2 is a schematic view of a plasma processing apparatus according toan embodiment of the present invention.

FIG. 3 is a schematic view of another plasma processing apparatusaccording to an embodiment of the present invention.

FIG. 4 is a schematic view of a conventional lower electrode structure.

FIG. 5 is a schematic view of another conventional lower electrodestructure.

BEST MODE FOR CARRYING OUT OF THE INVENTION

Now, embodiments of the present invention will be described morespecifically.

FIG. 1 is a schematic view of a lower electrode structure according toan embodiment of the present invention.

A lower electrode structure 1 shown in FIG. 1 is arranged in an chamberof a plasma processing apparatus such as a plasma etching apparatus andserves as a plasma formation electrode.

The lower electrode structure 1 has a base table formed of a conductivematerial such as aluminium, namely, a susceptor 2. On the susceptor 2,formed is an electrostatic chuck 3 (electrostatic adsorption member)having a dielectric layer 4 and a flat electrode 5 arranged inside thedielectric layer.

As materials for forming the dielectric layer 4, there are ceramic and aresin. The dielectric layer 4 formed of ceramic is particularlyeffective in this embodiment.

A pipe 6 for supplying a heat-transmitting gas such as helium (He) isvertically formed through the susceptor 2 and the dielectric layer 4.The pipe 6 is branched within the dielectric layer 4 and connected tonumerous holes (not shown) formed in the surface of the dielectric layer4. With this structure, the heat-transmitting gas such as helium gas issprayed out from the numerous holes to supply it to between thedielectric layer 4 and a substrate, such as a semiconductor substrate(hereinafter referred to as “wafer”) chucked on the dielectric layer 4.

To the flat electrode 5, an end of wiring 7 is connected. The other endof the wiring 7 is connected to a direct-current source 8. The wiring 7between the flat electrode 3 and the direct-current source 8 is equippedwith a low-pass filter 9. The low-pass filter 9 is constituted of acapacitor 16 and a resistance 17.

On the other hand, the wiring 10 is connected to the susceptor 2 at oneend via a capacitor 15 (described later). The other end of the wiring 10is connected to a high frequency source 11. The wiring 10 between thecapacitor 15 and the high frequency source 11 is provided with amatching box 12.

The wiring 7 and the wiring 10 are connected with a wiring element 14having a capacitor 13. Therefore, a high frequency voltage from the highfrequency source 11 is superimposed on the direct-current voltage to beapplied to the flat electrode 3 from the direct-current source 8. Morespecifically, the high frequency voltage is applied to both thesusceptor 2 and the flat electrode 3, whereas the direct-current voltageis not superimposed on the wiring 10 by the presence of the capacitor13.

In the conventional structure (FIG. 4) employing the dielectric layer103 formed of ceramic, when a high frequency of 2 MHz or less is appliedonly to the susceptor 101, formation of a high frequency electric fieldimmediately upon the wafer W is significantly prevented by thedielectric layer 103, as mentioned above. However, when a high frequencyvoltage is applied to the flat electrode 5 as is in this embodiment, theformation of the high frequency electric field is prevented only in theregion of the dielectric layer 4 between the flat electrode 5 and thewafer 6. In contrast, the formation of the high frequency electric fieldis not affected in the region of the dielectric layer 4 between the flatelectrode 5 and the susceptor 2.

Accordingly, when the high frequency voltage is applied to the flatelectrode 5, the effect of the dielectric layer 4 can be reducedcompared to the case where the high frequency voltage is applied only tothe susceptor 2. In other words, even in the case where the frequency ofthe high frequency power supplied from the high frequency source 11 is 2MHz or less and the dielectric layer is formed of ceramic, it ispossible to converge the high frequency electric field on the wafer W.As a result, a satisfactory high frequency electric field can be formed.

Furthermore, in a conventional case where a high frequency voltage isapplied to either the susceptor 2 or the flat electrode 5, the potentialdifference between the susceptor 2 and the flat electrode 3 periodicallyvaries. Therefore, if the maximum vale of the potential differenceexceeds the threshold, an abnormal discharge occurs in a pipe 6.

In contrast, in the aforementioned case, high frequency voltages havingthe same frequency are applied to both the susceptor 2 and the flatelectrode 3. Furthermore, the structure is designed such that adirect-current voltage is not superimposed on the side of the highfrequency source by the presence of the capacitor 13. Therefore, thephase difference of the high frequency voltage can be sufficientlyreduced. According to the arrangement of the structure, it is possibleto reduce the maximum value of the potential difference compared to thecase where a high frequency voltage is applied either one of thesusceptor 2 and the flat electrode 5. Hence, the occurrence of anabnormal discharge can be prevented.

The phase difference between the high frequency voltages to be appliedto the susceptor 2 and that to be applied to the flat electrode is notalways to be zero. However, when the phase difference is rendered zero,the maximum value of the potential difference can be further reduced,with the result that the potential difference between the susceptor 2and the flat electrode 5 can be always maintained at an extremely lowlevel. It is therefore possible to prevent occurrence of an abnormaldischarge more efficiently.

To allow the phase of the high frequency voltage to be applied to thesusceptor 2 to coincide with that to be applied to the flat electrode 3,the impedance from the connecting point of the wiring 10 to thesusceptor 2 and the wiring 14 may be allowed to coincide with that fromthe connecting point to the flat electrode 3.

For example, the impedances mentioned above may be allowed to coincidewith each other by interposing a capacitor 15, which has the samecapacitance as that of the capacitor 13, between the susceptor 2 and theconnecting point of the wiring 10 and the wiring 14. In this manner, thephase difference between the high frequency voltage to be applied to thesusceptor 2 and that to be applied to the flat electrode 3 can berendered zero.

According to the lower electrode structure 1 of this embodiment, asatisfactory high frequency electric field can be formed withoutoccurrence of an abnormal discharge even if the frequency of the highfrequency power supplied from the high frequency source 11 is 2 MHz orless.

For example, when the frequency of the high frequency power suppliedform the high frequency source 11 is 800 kHz, if the capacitance of acapacitor 16 constituting a filter 9 is set at 100 pF to 1000 pF, theresistivity of a resistance 17 is 1.5×10⁶Ω to 3×10⁶Ω, and each ofcapacitances of capacitors 13 and 15 is set at 10000 pF, the phasedifference between the high frequency voltage to be applied to thesusceptor 2 and that to be applied to the flat electrode 3 can berendered zero. As a result, a satisfactory high frequency electric fieldcan be formed on the wafer W. If the invention of this embodiment isapplied to plasma processing, satisfactory plasma characteristics can beobtained.

Now, a plasma processing apparatus using the lower electrode structure 1mentioned above will be explained.

FIG. 2 is a schematic view of a plasma processing apparatus according toan embodiment of the present invention. Note that this embodiment showsa plasma etching apparatus in which the lower electrode structure 1 isemployed.

In FIG. 2, a plasma etching apparatus 20 has an air-tight chamber 21. Aninsulating support board 22 is arranged at the bottom of the chamber 21.A cooling member 23 and a susceptor 2 are stacked on the support board22 in this order. An electrostatic chuck 3 formed on the upper surfaceof the susceptor 2. The electrostatic chuck 3 is constituted of adielectric layer 4 and a flat electrode 5 buried in the dielectric layer4. A wafer W is mounted on the dielectric layer 4.

A focus ring 24 is arranged on the dielectric layer 4 to surround thewafer W.

The cooling member 23 has a refrigerant circulating passage 25 formedtherein. A refrigerant is supplied to the refrigerant circulatingpassage 25 from outside the chamber 21 via a flow passage 26. Therefrigerant supplied to the refrigerant circulating passage 25 is usedfor cooling the wafer etc., and discharged from the chamber 21 to theoutside by way of a flow passage 27.

Furthermore, a pipe 28 is formed through the support board 22, coolingmember 23, the susceptor 2 and the dielectric layer 4, for supplyinghelium gas between the dielectric layer 4 and the wafer W.

In an upper portion of the chamber 21, a shower head 31 is arranged. Theshower head has numerous holes 30 on the surface facing the dielectriclayer 4. To the shower head 31, a gas supply source 34 is connected byway of pipes 32 and 33. The gas supply source 34 contains a process gassuch as CF₄, which is supplied to the chamber 21 by way of the pipe 33and the shower head 31. The pipe 33 is provided with a mass-flowcontroller 35 and a valve 36 in the order from the side of a gas supplysource 34. Incidentally, the shower head 31 is formed of a conductivematerial and serves as an upper electrode.

The pipe 32 for supplying the process gas to the shower head 31 iselectrically isolated from and the chamber 21 by an insulating member37.

A load-lock chamber 39 is arranged at a side of the chamber 21 with agate valve 38 interposed between them. The load-lock chamber 39 houses atransfer mechanism 40 which is formed a plurality of arms incombination. The transfer mechanism 40 is used for transferring a waferW between the load-lock chamber 39 and the chamber 21.

The chamber 21 and the load-lock chamber 39 have discharge ports 41 and42, respectively. The chamber 21 and the load-lock chamber 39 arevacuumed by a pump 43 through the discharge ports 41 and 42,respectively. As a result, desirable vacuum conditions are createdwithin the chamber 21 and the load-lock chamber 39.

An end of wiring 7 is connected to the flat electrode 5. The other endof the wiring is connected to a direct-current source 8. The wiring 7between the flat electrode 3 and the direct-current source 8 is providedwith a low-pass filter 9. On the other hand, one end of the wiring 10 isconnected to the susceptor 2 and the other end of the wiring 10 isconnected to a high frequency source 11.

Furthermore, the wiring 10 between the susceptor 2 and the highfrequency source 11 is provided with a phase shift circuit 50, anamplifier 51, a matching box 12 and a capacitor 15 sequentially in thisorder form the side of the high frequency source 11.

The wiring 7 is connected to the wiring 14 at a position between thelow-pass filter 9 and the flat electrode 3. The other end of the wiring14 is connected to the wiring 10 at a position between the matching box12 and the capacitor 15.

Therefore, a high frequency voltage from the high frequency source 11 issuperimposed on the direct-current voltage to be applied from the directcurrent source 8 to the flat electrode 3. More specifically, the highfrequency voltage is applied to both of the susceptor 2 and the flatelectrode 3. Note that the wiring 14 has a capacitor 13 between theconnecting point to the wiring 7 and that to the wiring 10. Therefore,the direct-current voltage is not superimposed on that of the wiring 10.

A wiring 52 is connected to the shower head 31 at one end. The other endof the wiring 52 is connected to the high frequency source 53. Anamplifier 54 and a matching box 55 are successively arranged between theshower head 31 and the high frequency source 53 in the order from theside of the high frequency source 53.

The phase of the high frequency to be applied from the high frequencysource 11 to the susceptor 2 by the phase shift circuit 50 is shifted byan angle of 180° with respect to the phase of the high frequency to beapplied from the high frequency source 53 to the shower head 31.

In the plasma etching apparatus 20 thus arranged, the wafer W is firsttransferred from the load-lock chamber 39 to the chamber 21 by thetransfer mechanism 40 and further placed on the dielectric layer 4. Notethat the load-lock chamber 39 and the chamber 21 have been evacuated bya pump 45 to a predetermined pressure.

Subsequently, a high frequency power having a frequency of 2 MHz orless, for example, 800 kHz, is supplied from the high frequency source11 to the susceptor 2. On the other hand, a high frequency power of13.56 MHz is supplied from the high frequency source 53 to the showerhead 31. In this case, if the capacitance of the capacitor 16constituting the low-pass filter 9 is set at 100 pF to 1000 pF, theresistivity of the resistor 17 at 1.5×10⁶Ω to 3×10⁶, and each of thecapacitances of the capacitors 13, 15 is set at 10000 pF, the phasedifference between the high frequency voltage to be applied to thesusceptor 2 and that to be applied to the flat electrode 3 can becontrolled to be zero, at the same time, a satisfactory high frequencyelectric field can be formed.

Furthermore, the valve 36 is opened under the aforementioned conditions,thereby supplying a process gas from the gas supply source 34 to theshower head 31 while controlling the flow rate by a mass-flow controller35. The process gas is converted into a plasma state by the highfrequency electric field between the shower head 31 and the susceptor 2.More specifically, a plasma is formed between the shower head 31 and thewafer W and used for etching the surface of the wafer W. The etching isperformed while supplying helium gas (He) between the dielectric layer 4and the wafer W by way of the pipe 28 and supplying a refrigerant fromthe flow passage 26 to a refrigerant circulating passage 25, whereby thetemperature of the wafer W can be controlled. In this manner, theetching rate can be accurately controlled.

Subsequently, another plasma processing apparatus using the lowerelectrode structure 1 shown in FIG. 1 will be explained.

FIG. 3 is a schematic view of another plasma etching apparatus accordingto the embodiment of the present invention. Note that FIG. 3 shows aplasma etching apparatus employing the present invention, in the same asin FIG. 2. In FIG. 3, like reference numerals are used to designate likestructural elements corresponding to those like in FIG. 2 and anyfurther explanation is omitted.

In the plasma etching apparatus 60 shown in FIG. 3, power is supplied ina different manner from in the plasma etching apparatus 20 shown in FIG.2. More specifically, in the plasma etching apparatus 60 shown in FIG.3, a high frequency power is supplied from the same high frequencysource 11 to both of the susceptor 2 and the shower head 31.

The high frequency power supplied from the high frequency source 11 isdivided by a variable trance 61 into the wiring 10 and the wiring 52.The high frequency power distributed to the wiring 10 passes through alow-pass filter 63 and then applied to the susceptor 2 and the flatelectrode 3 in the same manner explained in FIG. 2. On the other hand,the high frequency voltage distributed to the wiring 52 passes through alow-pass filter 63 and then applied to the shower head 31.

Etching using the plasma etching apparatus 60 is performed in accordancewith, for example, the method shown below.

To be more specific, the wafer W is transferred by the transfermechanism 40 from the lord-lock chamber 39 into the chamber 21 andfurther mounted on the dielectric layer 4. Note that the load-lockchamber 39 and the chamber 21 have been evacuated by the pump 45 to apredetermined pressure.

Subsequently, a high frequency power having a frequency of 2 MHz orless, for example, 380 kHz, is supplied from the high frequency source11 to the susceptor 2 and the shower head 31. In this case, the ratio ofthe power to be distributed to the wiring 52 to that to be distributedto the wiring 10 is for example, 6:4. Furthermore, if the capacitance ofthe capacitor 16 constituting the filter 9 is set at 100 pF to 1000 pF,the resistivity of the resistor 17 at 1.5×10⁶Ω to 3×10⁶Ω, and each ofthe capacitances of the capacitors 13, 15 is set at 10000 pF, the phasedifference between the high frequency voltage to be applied to thesusceptor 2 and that to be applied to the flat electrode 3 can becontrolled to be zero and a satisfactory high frequency electric fieldcan be formed.

Also in the plasma etching apparatus thus constituted, a reaction gas issupplied from the gas supply source 34 to the shower head 31 by openingthe valve 36 while controlling the flow rate by the mass-flow controller35 and supplying the high frequency as mentioned above. In this way, aplasma is formed between the shower head 31 and the susceptor 2 where ahigh frequency electric field is formed. As a result, the surface of thewafer W is etched.

Etching is performed while helium gas is supplied between the dielectriclayer 4 and the wafer W by way of the pipe 28 and a refrigerant issupplied from the flow passage 26 to the refrigerant circulating passage25. It is therefore possible to control the temperature of the wafer Wand thereby the etching rate is controlled with a high accuracy.

According to the plasma etching apparatus 60 shown in FIG. 3, a highfrequency voltage is applied from a single high frequency source to bothof the susceptor 2 and the shower head 31, so that the structure of thesystem can be simplified.

Note that the present invention is not limited to the embodiments andcan be modified in various ways.

In the embodiments mentioned above, we explained the case where thepresent invention is applied to a plasma etching apparatus. The presentinvention is not limited to these and applicable to other plasmaprocessing apparatuses including a plasma CVD.

INDUSTRIAL APPLICABILITY

When the lower electrode structure of the present invention is appliedto a plasma processing apparatus, a high frequency voltage is applied toboth of the base table and the flat electrode of the lower electricstructure. Therefore, a high frequency electric field can be morepreferably formed compared to a conventional case where a high frequencyvoltage is applied only to the base table.

According to the present invention, since a high frequency voltage isapplied to both of the base table and the flat electrode of the lowerelectrode structure, the phase difference between the high frequencyvoltages to be applied to the base table and the flat electrode can besufficiently reduced. Therefore, the potential difference between thebase table and the flat electrode can be maintained always low, with theresult that an abnormal discharge occurring when the potentialdifference between them exceeds a permissible value.

According to the present invention, there is provided a lower electrodestructure capable of forming a good high frequency electric fieldwithout causing an abnormal discharge while preventing the temperatureof a substrate to be processed from excessively increasing, and alsoprovided a plasma processing apparatus.

What is claimed is:
 1. A lower electrode structure for use in anapparatus in which plasma processing is applied to an substrate,comprising: a base table formed of a material having a conductivity; anelectrostatic adsorption member formed on the base table and having adielectric layer on which the substrate to be mounted and within whichan electrode electrically isolated from the base table is housed; firstwiring having an end connected to an electrode of the electrostaticadsorption member; a direct current source connected to the other end ofthe first wiring; a second wiring having an end connected to the basetable; a high frequency source connected to the other end of the secondwiring; a third wiring for connecting the first wiring to the secondwiring; a first capacitor formed on the third wiring; and a secondcapacitor formed on the second wiring and interposed between thesubstrate and a connecting point between the second wiring and the thirdwiring, wherein said second capacitor formed on the second wiring andthe first capacitor formed on the third wiring have the samecapacitance.
 2. The lower electrode structure according to claim 1,wherein the dielectric layer of the electrostatic adsorption material isformed of ceramic.
 3. The lower electrode structure according to claim1, comprising a gas supply means for supplying a heat-transmitting gasbetween the dielectric layer and the substrate from a lower portion ofthe base table via the electrostatic adsorption member.
 4. The lowerelectrode structure according to claim 1, further comprising a low-passfilter on the first wiring between the direct current source and thefirst capacitor.
 5. A plasma processing apparatus comprising: a chamberfor applying plasma processing to a substrate while holding airtight; alower electrode structure housed in the chamber and having a mountingsurface for the substrate; an upper electrode arranged in the chamber soas to face the mounting surface of the lower electrode structure; anevacuation system for evacuating the chamber; a process gas supplysystem for introducing a process gas into the chamber; said lowerelectrode structure comprising a base table formed of a conductivematerial a dielectric layer formed on the base table and having amounting surface for the substrate; an electrostatic adsorption memberformed within the dielectric layer and having an electrode electricallyisolated from the base table; first wiring having an end connected tothe electrode of the electrostatic adsorption member; a direct-currentsource connected to the other end of the first wiring; second wiringhaving an end connected to the base table; a high frequency sourceconnected to the other end of the second wiring; a third wiring forconnecting the first wiring and the second wiring; a first capacitorformed on the third wiring; a second capacitor formed on the secondwiring and interposed between the base table and a connection pointbetween the second wiring and the third wiring; wherein said secondcapacitor formed on the second wiring and the first capacitor formed onthe third wiring have the same capacitance.
 6. The plasma processingapparatus according to claim 5, wherein the dielectric layer of theelectrostatic adsorption member is formed of ceramic.
 7. The plasmaprocessing apparatus according to claim 5, comprising a gas supply meansfor supplying a heat-transmitting gas between the dielectric layer andthe substrate from a lower portion of the base table via theelectrostatic adsorption member.
 8. The plasma processing apparatusaccording to claim 5, further comprising a low-pass filter on the firstwiring between the direct current source and the first capacitor.
 9. Theplasma processing apparatus according to claim 5, further comprising ahigh frequency source for supplying a high frequency source to theopposite electrode.